The invention relates to a dispenser cathode comprising a heating element and a porous metal cathode body having in its pores a material for dispensing barium, barium oxide and scandium oxide.
Such cathodes are used, for example, in pickup tubes and picture display tubes, transmitter tubes, klystrons and travelling wave tubes.
Such a dispenser cathode is disclosed in U.S. Pat. No. 3,358,178. This patent describes a compressed dispenser cathode body composed of tungsten powder and Ba.sub.3 Sc.sub.4 O.sub.9. The Ba.sub.3 Sc.sub.4 O.sub.9 constitutes from 5 to 30% of the overall weight of the cathode body. Such a cathode is capable of emitting current at a density of 1.5 -4 A/cm.sup.2 at 1000.degree.-1100.degree. C. for a few thousand hours. However, there exists a need for cathodes having a longer life and better emission.
U.S. Pat. No. 4,007,393 discloses an impregnated dispenser cathode having as dispensing compounds BaO, CaO, Al.sub.2 O.sub.3 and Sc.sub.2 O.sub.3. This cathode can provide a current density of 5 A/cm.sup.2 at 1000.degree. C. for approximately 3000 hours.